1. Field of the Invention
The invention involves a pulse-compression, MTI, doppler-radar system for determining target velocity information from a single, frequency-coded uncompressed transmitted pulse. More specifically, the first and second halves of the uncompressed pulse (hereinafter target-return pulse), coded with even and odd harmonic sidebands of a pulse repetition center frequency, respectively, are pulse-compressed simultaneously and the phase difference therebetween compared to determine target velocity information.
2. Description of the Prior Art
Conventional moving-target indicators require that a radar or sonar transmit several sequential pulses of the same frequency to obtain target velocity information. It would be desirable to obtain such information from one pulse since this would allow the radar frequency to be changed on every pulse and thereby avoid jamming.
To solve this problem, phase-coded matched filters for pulse-compression, MTI, doppler-radar systems have been proposed that would act as doppler-filter banks yielding relatively coarse target velocity information on a single echo pulse. The theory for such a system is described in "Radar Signals", Cook and Bernfield, Academic Press, 1967, pp. 287-293. Such a system may determine between which pair of target blind speeds a target velocity may lie, but cannot specifically determine the exact target velocity.
This system is improved upon by copending Navy Case No. 60,003, U.S. application Ser. No. 700,925 entitled "Phase-coded Monopulse MTI" which describes a pulse-compression, MTI, doppler-radar system for determining target velocity information from a single, phase-coded uncompressed transmitted pulse. The system includes a pulse-compression filter consisting of at least two pulse compressors and a phase-comparison processor. The pulse compressors simultaneously pulse-compress separate portions of the single, phase-coded target-return pulse. The phase-comparison processor then determines the phase difference between the compressed pulses to obtain the target velocity information. This system determines target velocity from one target return pulse, but does not optimize the rejection of distributed clutter. More specifically, in a phase-coded system distributed clutter from the entire uncompressed pulse length contributes to pulse compressor sidelobes. This means that for a pulse compression ratio of N, there must be N phase-coded segments in the uncompressed pulse and N processing channels (i.e., time delay and weighter) to achieve good distributed clutter rejection.
What is needed is a pulse compression, MTI, doppler-radar system which will determine target velocity information from a single target-return pulse but will provide better rejection of distributed clutter and require fewer coded segments in the uncompressed pulse. As a result, fewer processing channels will be needed and equipment requirements will be simplified.